48 lines
1.5 KiB
Markdown
48 lines
1.5 KiB
Markdown
# Internet protocol Version 4 (IPV4)
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- IP is the principal communications protocol in the network layer.
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- IP has the task of delivering packets from source host to destination host based on IP addresses.
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IP defines datagram structure that encapsulate the data to be delivered.
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An IP datagram (packet) consists of a header part an a text part. (payload)
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The header has a 20 byte fixed part an a variable length optional part.
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![[IP-packet.png]]
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Some of the fields in a packet are not always used.
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## Packet encapsulation
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Packets are encapsulated in data link frames (Ethernet)
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![[packet-enscapsulation-2.png]]
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## Fragmentation
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Mostly, data link frames are smaller in size than IP Packets
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So the IP Packet does not fit in the data link frame.
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In these cases the packet is split up into multiple parts (fragments) and each fragment is send in a separate frame.
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![[packet-fragmentation.png]]
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The receiver host then combines all fragments before using them
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Therefore the receiver should know which part of the message each fragment belongs (hence the fragment offset field in IP header)
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![[packet-fragmentation-2.png]]
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Ecapsulating a packet in a frame requires:
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- Sender MAC Address (can be found out)
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- Receiver MAC Address (Should be found out
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## Dynamic Host Control Protocol (DHCP)
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Address allocation can happen trough 2 ways.
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Fixed allocation:
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- Wastefull because if a hosts is not active the IP Address is still allocated.
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Dynamic allocation:
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- A DHCP server manages the allocation of IP Addresses and leases them for a certain amount of time.
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